Practical ways to improve water quality
Salinas/Castroville area ditches, creeks and sloughsAverage of 2005-07 monthly sampling of 11 sites
W t lit M t E d 2005 2007Water quality parameter
Measurement unit
Exceedance threshold
2005-2007 monthly average
NO3-N PPM > 10 25PO4-P PPM > 0.5 0.63Algae % survival > 110 228
Turbidity NTU > 50 587Water toxicity % survival < 80 27ySediment toxicity % survival < 80 24
Source of nutrients ?Source of nutrients ?FertilizerWell water
What soluble nutrient load does vegetable field runoff carry ?
In 13 Salinas Valley trials …
PPMNO3-N PO4-PNO3-N PO4-P
Low 1 0.1High 48 2 1High 48 2.1Mean 12 0.7
How about drain tile effluent ?How about drain tile effluent ?
2002-04 drain tile sampling in the Salinas Valley
Why is drain tile effluent so high in NO3-N?all NO3-N is in the soil solution
Relationship of soil NO3-N to soil solution NO3-N :
Soil NO3-N NO3-N in soil solution (PPM)(PPM) Sandy loam Clay( ) y y
10 50 30
In 13 Salinas Valley field trials runoff turbidity rangedfrom 200 - 4,600 NTU
Bottom line :Any water escaping from a vegetable field is likely to exceed
t lit t d d f ll t twater quality standards for one or more pollutants
What can be done ?Treat the water to remove pollutantsReduce the application of materials that can move in waterReduce the volume of water that leaves the field
Water treatment :
Consistently reduce sediment lossMinimally effective for soluble nutrientsMay conflict with microbial food safety practices
Water treatment :
PAMPAM
Water treatment :
PAM
Highly effective for sediment removalRelatively inexpensive, can be automatedInconsistently effective at reducing soluble nutrients
Most practical solution is to limitthe volume of runoff or leachate …
… and drip irrigation is the ideal tool
Crop water use can be predicted by canopy size and ETo :
80
100
over
40
60
80
t can
opy
coor
lettu
ce
0
20
1 2 3 4 5 6 7 8 9 10
Perc
ent fo
1 2 3 4 5 6 7 8 9 10
Weeks after planting
Irrigation requirementIrrigation requirement can be predicted by canopy size and ETo :
100120
To
406080
rcen
t of E
Tfo
r let
tuce
020
1 2 3 4 5 6 7 8 9 10
Per f
Efficient seasonal drip irrigation volume ≈ 80 – 120 % of ETo
Weeks after planting
250ied
Drip irrigation management varies greatly among growers :
150
200
250
ETo a
ppli
rip
50
100
150
easo
nal E
with
dr
Ideal zone
0
50
1 2 3 4 5 6 7 8 9 10 11 12 13 14% o
f se
Commercial field
Drip-irrigated lettuce fields in the Salinas Valley
250lied
Consequences of excessive irrigation :
150
200
ETo a
ppl
drip
50
100
50
easo
nal E
with
d
Ideal zone
0
50
1 2 3 4 5 6 7 8 9 10 11 12 13 14% o
f se
Commercial field
Assume early summer conditions northern Salinas Valley locationAssume early summer conditions, northern Salinas Valley location,sandy loam soil :
If field 5 applied 5 inches of water with drip, h fi ld 14 li d 10 i hthen field 14 applied 10 inches
If soil is 10 PPM NO3-N, field 14 lost > 50 lb N/acre in leaching !
Long irrigation intervals ruin drip irrigation efficiency :
In drip-irrigated celery fields …
8
10ys
io
ns
4
6
rage
day
n irr
igat
2
4
Ave
rbe
twee
n
01 2 3 4 5 6 7 8 9
Field
Long irrigation intervals lead toheavy individual applications :heavy individual applications :
1.5
2
ches
ion
Light soilHeavy soil
0 5
1
erag
e in
cer
irrig
at
Maximum for efficient irrigation
0
0.5
1 2 3 4 5 6 7 8 9
Ave pe efficient irrigation
1 2 3 4 5 6 7 8 9
Field
Above this maximum range the leaching fraction becomes significant !
What constitutes efficient fertigation ?
30
202530
upta
ke/ w
eek)
51015
ettu
ce N
lb
/ ac
re
90 - 120 lb N/acreat harvest
01 2 3 4 5 6 7 8 9 10
W k ft l ti
Le (l
Weeks after planting
202530
ptak
ew
eek)
101520
tuce
N u
p/ a
cre
/ w90 - 120 lb N/acre
at harvest
05
1 2 3 4 5 6 7 8 9 10
Lett
(lb
Weeks after planting
40
20
30
N u
ptak
ere
/ w
eek)
180 - 220 lb N/acre
0
10
20
Cel
ery
N (l
b / a
cr 180 220 lb N/acreat harvest
01 2 3 4 5 6 7 8 9 10 11 12
Weeks after transplanting
2007 lettuce fertigation trials :
FieldFieldFieldLettuce Lettuce Lettuce
typetypetypeSoil NOSoil NOSoil NO333---N at startN at startN at startof fertigation (PPM)of fertigation (PPM)of fertigation (PPM)g ( )g ( )g ( )
111 headheadhead 202020222 headheadhead 272727333 romaineromaineromaine 212121
2007 lettuce fertigation trials :
Reference evapotranspiration Drip irrigation Field (ETo , inches) applied (inches)
1 6.2 4.92 6 5 4 72 6.5 4.73 2.4 2.8
6080
gatio
ncr
e)
field 1
12 f
02040
25 30 35 40 45 50 55 60 65
N fe
rtig
(lb/
ac 127 lb N fertigated
25 30 35 40 45 50 55 60 65
Days after planting
153 lb N fertigated406080
gatio
ncr
e)
field 2
153 lb N fertigated
02040
25 30 35 40 45 50 55 60 65
N fe
rtig
(lb/
ac
67 lb N f ti t d
25 30 35 40 45 50 55 60 65
Days after planting
60
80
atio
nre
)
field 3
67 lb N fertigated
0
20
40
N fe
rtig
a (l
b/ac
r
25 30 35 40 45 50 55 60 65Days after planting
80n field 1
Reduced N treatment created by eliminating some N fertigation :
0204060
N fe
rtig
atio
n (l
b/ac
re) field 1
x x0
25 30 35 40 45 50 55 60 65
Days after planting
N
80n field 2
0204060
N fe
rtig
atio
(lb/
acre
) field 2
xx
025 30 35 40 45 50 55 60 65
Days after planting
N
80
n field 3
20
40
60
N fe
rtig
atio
(lb/
acre
)
x0
25 30 35 40 45 50 55 60 65Days after planting
Results :
lb N / acreMean
plant wtCrop N uptake
Field Treatment total fertigated (lb) (lb / acre)Field Treatment total fertigated (lb) (lb / acre)1 Grower 169 127 2.29 98
Reduced N 92 50 2.31 91
Results :
lb N / acreMean
plant wtCrop N uptake
Field Treatment total fertigated (lb) (lb / acre)Field Treatment total fertigated (lb) (lb / acre)1 Grower 169 127 2.29 98
Reduced N 92 50 2.31 91
2 Grower 171 153 2.16 103Reduced N 64 46 2 27 101Reduced N 64 46 2.27 101
Results :
lb N / acreMean
plant wtCrop N uptake
Field Treatment total fertigated (lb) (lb / acre)Field Treatment total fertigated (lb) (lb / acre)1 Grower 169 127 2.29 98
Reduced N 92 50 2.31 91
2 Grower 171 153 2.16 103Reduced N 64 46 2 27 101Reduced N 64 46 2.27 101
3 Grower 115 67 1.92 102Reduced N 67 19 1.81 87
Conclusion :given careful irrigation, a modest level of N fertigation is sufficient
What will efficient fertilization do to water quality ?Reduced N application limits potential N lossReduced N application limits potential N loss
What will efficient irrigation do to water quality ?N concentration of runoff or leachate might increase but
concentration x volume = load
N concentration of runoff or leachate might increase, butenvironmental load will decrease substantially
What will efficient irrigation do to water quality ?N concentration of runoff or leachate might increase but
concentration x volume = load
N concentration of runoff or leachate might increase, butenvironmental load will decrease substantially
Example : lettuce field 14 – 230% of ET appliedExample : lettuce field 14 230% of ETo applied50 PPM soil solution NO3-N in 5 inches of leaching = 57 lb N/acre
Example 2: lettuce field 5 – 110% of ETo applied100 PPM soil solution NO3-N in 0.5 inches of water loss = 11 lb N/acre3
Putting it together:Minimize and/or treat sprinkler irrigation during crop establishmentDrip irrigate based on ET, with irrigation frequent enough to be efficient Fertigate modestl timing N application to meet crop ptakeFertigate modestly, timing N application to meet crop uptake
What about winter ?Leave as little NO3-N in the profile as possible after fall cropLeave as little NO3 N in the profile as possible after fall cropEmploy winter cover where practical